Cisplatin, a long-known anticancer agent, has a four-coordinate square planar, very simple structure in which ammonia molecules and chloride ions are coordinated to divalent platinum in a cis-configuration. This anticancer agent is useful and continues to be used in clinical practice today.
Following cisplatin, a variety of anticancer agents have been developed. In Japan, carboplatin, nedaplatin, and oxaliplatin have been used in clinical applications.
Metal complexes, which comprise a metal ion and one or more organic substances, provide a potential for elucidating the role and biological mechanism of trace metal ions, which are essential for life activity, and have thus had a significant impact on recent development in bioscience. Research on the behavior of metal ions in animals and humans, and on the benefits of metal ions as a medical drug, was initiated already several decades ago. Chemists, pharmacologists, and medical scientists have collaborated and developed a new academic field, namely, inorganic pharmacology.
Sugar plays in vivo a vital role for life activity, such as in energy storage, structure-building materials, and molecular recognition, as well as an energy source. Chitin and chitosan are polymeric glucosamine into which amine is introduced, and thus have increased coordinating power as compared with glucose. Chitin and chitosan are the major components of crustacean exoskeletons, and the most abundant after cellulose. Despite the fact that glucosamine is such an essential sugar, there are limited reports about complexes containing glucosamine as a ligand. In particular, there are few reports on noble metal complexes containing glucosamine as a ligand.
Non-patent Documents 1 to 4 report on novel platinum complexes that have various sugar backbones. The platinum complexes disclosed in these documents have a structure in which the platinum atom is coordinated with two chloride ions or two iodide ions.
Non-patent Document 1 reports on the synthesis and antitumor activity of platinum(II) diamino sugar complexes. Non-patent Document 2 reports that mono and dihydroxy diamino tetrahydropyran derivatives were prepared and converted into the corresponding diamino cis-platinum analogs, and that their antitumor activity was evaluated. Non-patent Document 3 reports on the synthesis and antitumor activity of platinum complexes containing one or more platinum centers bound to sucrose-derived ligands. Non-patent Document 4 reports on the synthesis and cytotoxicity of a carbohydrate-linked cisplatin analogue.
Non-patent Documents 5 to 7 disclose platinum or palladium complexes that have a structure in which the metal atom is coordinated with three atoms (N and S) and one chloride ion. Non-patent Document 8 reports on the synthesis of DMSO complexes of platinum(II) and palladium(II).